Negative differential resistance (NDR) devices have tremendous potential for low-power memory, logic, and mixed circuit applications. However, typical successful demonstrations of room temperature NDR suitable for circuit applications has involved rigid inorganic semiconductors, such as devices comprising silicon and silicon-germanium alloys, III-V compound semiconductors, or so forth. These rigid inorganic semiconductors are not conducive to incorporation in flexible memory devices such as Smartcard technology for portable storage of banking and medical information.
Advantageously, the N-shaped electrical characteristics of two serially connected NDR devices can be exploited to form a latch or memory device having two stable latching points. When this pair is fashioned into a one transistor tunneling diode static random access memory (1T TSRAM) cell utilizing NDR devices with extremely low valley current densities, the number of devices needed and the standby power consumption are greatly decreased from traditional six transistor SRAM memory. More generally, one or more NDR devices can be operatively coupled with at least one additional electrical element (typically a transistor, resistor, or the like defining a load) to define a latching or memory element having two or more stable states. For room temperature latching or memory operation, the NDR device should exhibit room temperature NDR operation with a reasonably high peak-to-valley current ratio (PVCR), such as PVCR values of about 2-3 or higher. Similarly, mixed-signal receiver circuits can be constructed using an NDR device to perform an analog-to-digital conversion by latching to various states. An RF oscillator source can also be fashioned by biasing in the NDR region to oscillate in this unstable region. With suitable circuitry, a compact voltage controlled oscillator can be constructed so that the RF output can be tuned.
NDR has been observed in molecular devices using molecules as the active material. However, these devices typically exhibit limited yield and repeatability. Moreover, the current-voltage shape for such molecular devices is typically not well-suited for providing robust latching behavior for latching or memory devices.